RFC1831: RPC: Remote Procedure Call Protocol Specification Version 2

Network Working Group R. Srinivasan
Request for Comments: 1831 Sun Microsystems
Category: Standards Track August 1995
RPC: Remote Procedure Call Protocol Specification Version 2
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
ABSTRACT
This document describes the ONC Remote Procedure Call (ONC RPC
Version 2) protocol as it is currently deployed and accepted. "ONC"
stands for "Open Network Computing".
TABLE OF CONTENTS
1. INTRODUCTION 2
2. TERMINOLOGY 2
3. THE RPC MODEL 2
4. TRANSPORTS AND SEMANTICS 4
5. BINDING AND RENDEZVOUS INDEPENDENCE 5
6. AUTHENTICATION 5
7. RPC PROTOCOL REQUIREMENTS 5
7.1 RPC Programs and Procedures 6
7.2 Authentication 7
7.3 Program Number Assignment 8
7.4 Other Uses of the RPC Protocol 8
7.4.1 Batching 8
7.4.2 Broadcast Remote Procedure Calls 8
8. THE RPC MESSAGE PROTOCOL 9
9. AUTHENTICATION PROTOCOLS 12
9.1 Null Authentication 13
10. RECORD MARKING STANDARD 13
11. THE RPC LANGUAGE 13
11.1 An Example Service Described in the RPC Language 13
11.2 The RPC Language Specification 14
11.3 Syntax Notes 15
APPENDIX A: SYSTEM AUTHENTICATION 16
REFERENCES 17
Security Considerations 18
Author's Address 18
Srinivasan Standards Track [Page 1]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
1. INTRODUCTION
This document specifies version two of the message protocol used in
ONC Remote Procedure Call (RPC). The message protocol is specified
with the eXternal Data Representation (XDR) language [9]. This
document assumes that the reader is familiar with XDR. It does not
attempt to justify remote procedure calls systems or describe their
use. The paper by Birrell and Nelson [1] is recommended as an
excellent background for the remote procedure call concept.
2. TERMINOLOGY
This document discusses clients, calls, servers, replies, services,
programs, procedures, and versions. Each remote procedure call has
two sides: an active client side that makes the call to a server,
which sends back a reply. A network service is a collection of one
or more remote programs. A remote program implements one or more
remote procedures; the procedures, their parameters, and results are
documented in the specific program's protocol specification. A
server may support more than one version of a remote program in order
to be compatible with changing protocols.
For example, a network file service may be composed of two programs.
One program may deal with high-level applications such as file system
access control and locking. The other may deal with low-level file
input and output and have procedures like "read" and "write". A
client of the network file service would call the procedures
associated with the two programs of the service on behalf of the
client.
The terms client and server only apply to a particular transaction; a
particular hardware entity (host) or software entity (process or
program) could operate in both roles at different times. For
example, a program that supplies remote execution service could also
be a client of a network file service.
3. THE RPC MODEL
The ONC RPC protocol is based on the remote procedure call model,
which is similar to the local procedure call model. In the local
case, the caller places arguments to a procedure in some well-
specified location (such as a register window). It then transfers
control to the procedure, and eventually regains control. At that
point, the results of the procedure are extracted from the well-
specified location, and the caller continues execution.
Srinivasan Standards Track [Page 2]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
The remote procedure call model is similar. One thread of control
logically winds through two processes: the caller's process, and a
server's process. The caller process first sends a call message to
the server process and waits (blocks) for a reply message. The call
message includes the procedure's parameters, and the reply message
includes the procedure's results. Once the reply message is
received, the results of the procedure are extracted, and caller's
execution is resumed.
On the server side, a process is dormant awaiting the arrival of a
call message. When one arrives, the server process extracts the
procedure's parameters, computes the results, sends a reply message,
and then awaits the next call message.
In this model, only one of the two processes is active at any given
time. However, this model is only given as an example. The ONC RPC
protocol makes no restrictions on the concurrency model implemented,
and others are possible. For example, an implementation may choose
to have RPC calls be asynchronous, so that the client may do useful
work while waiting for the reply from the server. Another
possibility is to have the server create a separate task to process
an incoming call, so that the original server can be free to receive
other requests.
There are a few important ways in which remote procedure calls differ
from local procedure calls:
1. Error handling: failures of the remote server or network must
be handled when using remote procedure calls.
2. Global variables and side-effects: since the server does not
have access to the client's address space, hidden arguments cannot
be passed as global variables or returned as side effects.
3. Performance: remote procedures usually operate one or more
orders of magnitude slower than local procedure calls.
4. Authentication: since remote procedure calls can be transported
over unsecured networks, authentication may be necessary.
Authentication prevents one entity from masquerading as some other
entity.
The conclusion is that even though there are tools to automatically
generate client and server libraries for a given service, protocols
must still be designed carefully.
Srinivasan Standards Track [Page 3]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
4. TRANSPORTS AND SEMANTICS
The RPC protocol can be implemented on several different transport
protocols. The RPC protocol does not care how a message is passed
from one process to another, but only with specification and
interpretation of messages. However, the application may wish to
obtain information about (and perhaps control over) the transport
layer through an interface not specified in this document. For
example, the transport protocol may impose a restriction on the
maximum size of RPC messages, or it may be stream-oriented like TCP
with no size limit. The client and server must agree on their
transport protocol choices.
It is important to point out that RPC does not try to implement any
kind of reliability and that the application may need to be aware of
the type of transport protocol underneath RPC. If it knows it is
running on top of a reliable transport such as TCP [6], then most of
the work is already done for it. On the other hand, if it is running
on top of an unreliable transport such as UDP [7], it must implement
its own time-out, retransmission, and duplicate detection policies as
the RPC protocol does not provide these services.
Because of transport independence, the RPC protocol does not attach
specific semantics to the remote procedures or their execution
requirements. Semantics can be inferred from (but should be
explicitly specified by) the underlying transport protocol. For
example, consider RPC running on top of an unreliable transport such
as UDP. If an application retransmits RPC call messages after time-
outs, and does not receive a reply, it cannot infer anything about
the number of times the procedure was executed. If it does receive a
reply, then it can infer that the procedure was executed at least
once.
A server may wish to remember previously granted requests from a
client and not regrant them in order to insure some degree of
execute-at-most-once semantics. A server can do this by taking
advantage of the transaction ID that is packaged with every RPC
message. The main use of this transaction ID is by the client RPC
entity in matching replies to calls. However, a client application
may choose to reuse its previous transaction ID when retransmitting a
call. The server may choose to remember this ID after executing a
call and not execute calls with the same ID in order to achieve some
degree of execute-at-most-once semantics. The server is not allowed
to examine this ID in any other way except as a test for equality.
On the other hand, if using a "reliable" transport such as TCP, the
application can infer from a reply message that the procedure was
executed exactly once, but if it receives no reply message, it cannot
Srinivasan Standards Track [Page 4]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
assume that the remote procedure was not executed. Note that even if
a connection-oriented protocol like TCP is used, an application still
needs time-outs and reconnection to handle server crashes.
There are other possibilities for transports besides datagram- or
connection-oriented protocols. For example, a request-reply protocol
such as VMTP [2] is perhaps a natural transport for RPC. ONC RPC
uses both TCP and UDP transport protocols. Section 10 (RECORD
MARKING STANDARD) describes the mechanism employed by ONC RPC to
utilize a connection-oriented, stream-oriented transport such as TCP.
5. BINDING AND RENDEZVOUS INDEPENDENCE
The act of binding a particular client to a particular service and
transport parameters is NOT part of this RPC protocol specification.
This important and necessary function is left up to some higher-level
software.
Implementors could think of the RPC protocol as the jump-subroutine
instruction ("JSR") of a network; the loader (binder) makes JSR
useful, and the loader itself uses JSR to accomplish its task.
Likewise, the binding software makes RPC useful, possibly using RPC
to accomplish this task.
6. AUTHENTICATION
The RPC protocol provides the fields necessary for a client to
identify itself to a service, and vice-versa, in each call and reply
message. Security and access control mechanisms can be built on top
of this message authentication. Several different authentication
protocols can be supported. A field in the RPC header indicates
which protocol is being used. More information on specific
authentication protocols is in section 9: "Authentication Protocols".
7. RPC PROTOCOL REQUIREMENTS
The RPC protocol must provide for the following:
(1) Unique specification of a procedure to be called.
(2) Provisions for matching response messages to request messages.
(3) Provisions for authenticating the caller to service and
vice-versa.
Srinivasan Standards Track [Page 5]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
Besides these requirements, features that detect the following are
worth supporting because of protocol roll-over errors, implementation
bugs, user error, and network administration:
(1) RPC protocol mismatches.
(2) Remote program protocol version mismatches.
(3) Protocol errors (such as misspecification of a procedure's
parameters).
(4) Reasons why remote authentication failed.
(5) Any other reasons why the desired procedure was not called.
7.1 RPC Programs and Procedures
The RPC call message has three unsigned integer fields -- remote
program number, remote program version number, and remote procedure
number -- which uniquely identify the procedure to be called.
Program numbers are administered by a central authority
(rpc@sun.com). Once implementors have a program number, they can
implement their remote program; the first implementation would most
likely have the version number 1. Because most new protocols evolve,
a version field of the call message identifies which version of the
protocol the caller is using. Version numbers enable support of both
old and new protocols through the same server process.
The procedure number identifies the procedure to be called. These
numbers are documented in the specific program's protocol
specification. For example, a file service's protocol specification
may state that its procedure number 5 is "read" and procedure number
12 is "write".
Just as remote program protocols may change over several versions,
the actual RPC message protocol could also change. Therefore, the
call message also has in it the RPC version number, which is always
equal to two for the version of RPC described here.
The reply message to a request message has enough information to
distinguish the following error conditions:
(1) The remote implementation of RPC does not support protocol
version 2. The lowest and highest supported RPC version numbers
are returned.
(2) The remote program is not available on the remote system.
(3) The remote program does not support the requested version
number. The lowest and highest supported remote program version
numbers are returned.
Srinivasan Standards Track [Page 6]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
(4) The requested procedure number does not exist. (This is
usually a client side protocol or programming error.)
(5) The parameters to the remote procedure appear to be garbage
from the server's point of view. (Again, this is usually caused
by a disagreement about the protocol between client and service.)
7.2 Authentication
Provisions for authentication of caller to service and vice-versa are
provided as a part of the RPC protocol. The call message has two
authentication fields, the credential and verifier. The reply
message has one authentication field, the response verifier. The RPC
protocol specification defines all three fields to be the following
opaque type (in the eXternal Data Representation (XDR) language [9]):
enum auth_flavor {
AUTH_NONE = 0,
AUTH_SYS = 1,
AUTH_SHORT = 2
/* and more to be defined */
};
struct opaque_auth {
auth_flavor flavor;
opaque body<400>;
};
In other words, any "opaque_auth" structure is an "auth_flavor"
enumeration followed by up to 400 bytes which are opaque to
(uninterpreted by) the RPC protocol implementation.
The interpretation and semantics of the data contained within the
authentication fields is specified by individual, independent
authentication protocol specifications. (Section 9 defines the
various authentication protocols.)
If authentication parameters were rejected, the reply message
contains information stating why they were rejected.
Srinivasan Standards Track [Page 7]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
7.3 Program Number Assignment
Program numbers are given out in groups of hexadecimal 20000000
(decimal 536870912) according to the following chart:
0 - 1fffffff defined by rpc@sun.com
20000000 - 3fffffff defined by user
40000000 - 5fffffff transient
60000000 - 7fffffff reserved
80000000 - 9fffffff reserved
a0000000 - bfffffff reserved
c0000000 - dfffffff reserved
e0000000 - ffffffff reserved
The first group is a range of numbers administered by rpc@sun.com and
should be identical for all sites. The second range is for
applications peculiar to a particular site. This range is intended
primarily for debugging new programs. When a site develops an
application that might be of general interest, that application
should be given an assigned number in the first range. Application
developers may apply for blocks of RPC program numbers in the first
range by sending electronic mail to "rpc@sun.com". The third group
is for applications that generate program numbers dynamically. The
final groups are reserved for future use, and should not be used.
7.4 Other Uses of the RPC Protocol
The intended use of this protocol is for calling remote procedures.
Normally, each call message is matched with a reply message.
However, the protocol itself is a message-passing protocol with which
other (non-procedure call) protocols can be implemented.
7.4.1 Batching
Batching is useful when a client wishes to send an arbitrarily large
sequence of call messages to a server. Batching typically uses
reliable byte stream protocols (like TCP) for its transport. In the
case of batching, the client never waits for a reply from the server,
and the server does not send replies to batch calls. A sequence of
batch calls is usually terminated by a legitimate remote procedure
call operation in order to flush the pipeline and get positive
acknowledgement.
7.4.2 Broadcast Remote Procedure Calls
In broadcast protocols, the client sends a broadcast call to the
network and waits for numerous replies. This requires the use of
packet-based protocols (like UDP) as its transport protocol. Servers
Srinivasan Standards Track [Page 8]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
that support broadcast protocols usually respond only when the call
is successfully processed and are silent in the face of errors, but
this varies with the application.
The principles of broadcast RPC also apply to multicasting - an RPC
request can be sent to a multicast address.
8. THE RPC MESSAGE PROTOCOL
This section defines the RPC message protocol in the XDR data
description language [9].
enum msg_type {
CALL = 0,
REPLY = 1
};
A reply to a call message can take on two forms: The message was
either accepted or rejected.
enum reply_stat {
MSG_ACCEPTED = 0,
MSG_DENIED = 1
};
Given that a call message was accepted, the following is the status
of an attempt to call a remote procedure.
enum accept_stat {
SUCCESS = 0, /* RPC executed successfully */
PROG_UNAVAIL = 1, /* remote hasn't exported program */
PROG_MISMATCH = 2, /* remote can't support version # */
PROC_UNAVAIL = 3, /* program can't support procedure */
GARBAGE_ARGS = 4, /* procedure can't decode params */
SYSTEM_ERR = 5 /* errors like memory allocation failure */
};
Reasons why a call message was rejected:
enum reject_stat {
RPC_MISMATCH = 0, /* RPC version number != 2 */
AUTH_ERROR = 1 /* remote can't authenticate caller */
};
Why authentication failed:
enum auth_stat {
AUTH_OK = 0, /* success */
Srinivasan Standards Track [Page 9]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
/*
* failed at remote end
*/
AUTH_BADCRED = 1, /* bad credential (seal broken) */
AUTH_REJECTEDCRED = 2, /* client must begin new session */
AUTH_BADVERF = 3, /* bad verifier (seal broken) */
AUTH_REJECTEDVERF = 4, /* verifier expired or replayed */
AUTH_TOOWEAK = 5, /* rejected for security reasons */
/*
* failed locally
*/
AUTH_INVALIDRESP = 6, /* bogus response verifier */
AUTH_FAILED = 7 /* reason unknown */
};
The RPC message:
All messages start with a transaction identifier, xid, followed by a
two-armed discriminated union. The union's discriminant is a
msg_type which switches to one of the two types of the message. The
xid of a REPLY message always matches that of the initiating CALL
message. NB: The xid field is only used for clients matching reply
messages with call messages or for servers detecting retransmissions;
the service side cannot treat this id as any type of sequence number.
struct rpc_msg {
unsigned int xid;
union switch (msg_type mtype) {
case CALL:
call_body cbody;
case REPLY:
reply_body rbody;
} body;
};
Body of an RPC call:
In version 2 of the RPC protocol specification, rpcvers must be equal
to 2. The fields prog, vers, and proc specify the remote program,
its version number, and the procedure within the remote program to be
called. After these fields are two authentication parameters: cred
(authentication credential) and verf (authentication verifier). The
two authentication parameters are followed by the parameters to the
remote procedure, which are specified by the specific program
protocol.
The purpose of the authentication verifier is to validate the
authentication credential. Note that these two items are
Srinivasan Standards Track [Page 10]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
historically separate, but are always used together as one logical
entity.
struct call_body {
unsigned int rpcvers; /* must be equal to two (2) */
unsigned int prog;
unsigned int vers;
unsigned int proc;
opaque_auth cred;
opaque_auth verf;
/* procedure specific parameters start here */
};
Body of a reply to an RPC call:
union reply_body switch (reply_stat stat) {
case MSG_ACCEPTED:
accepted_reply areply;
case MSG_DENIED:
rejected_reply rreply;
} reply;
Reply to an RPC call that was accepted by the server:
There could be an error even though the call was accepted. The first
field is an authentication verifier that the server generates in
order to validate itself to the client. It is followed by a union
whose discriminant is an enum accept_stat. The SUCCESS arm of the
union is protocol specific. The PROG_UNAVAIL, PROC_UNAVAIL,
GARBAGE_ARGS, and SYSTEM_ERR arms of the union are void. The
PROG_MISMATCH arm specifies the lowest and highest version numbers of
the remote program supported by the server.
struct accepted_reply {
opaque_auth verf;
union switch (accept_stat stat) {
case SUCCESS:
opaque results[0];
/*
* procedure-specific results start here
*/
case PROG_MISMATCH:
struct {
unsigned int low;
unsigned int high;
} mismatch_info;
default:
/*
Srinivasan Standards Track [Page 11]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
* Void. Cases include PROG_UNAVAIL, PROC_UNAVAIL,
* GARBAGE_ARGS, and SYSTEM_ERR.
*/
void;
} reply_data;
};
Reply to an RPC call that was rejected by the server:
The call can be rejected for two reasons: either the server is not
running a compatible version of the RPC protocol (RPC_MISMATCH), or
the server rejects the identity of the caller (AUTH_ERROR). In case
of an RPC version mismatch, the server returns the lowest and highest
supported RPC version numbers. In case of invalid authentication,
failure status is returned.
union rejected_reply switch (reject_stat stat) {
case RPC_MISMATCH:
struct {
unsigned int low;
unsigned int high;
} mismatch_info;
case AUTH_ERROR:
auth_stat stat;
};
9. AUTHENTICATION PROTOCOLS
As previously stated, authentication parameters are opaque, but
open-ended to the rest of the RPC protocol. This section defines two
standard "flavors" of authentication. Implementors are free to
invent new authentication types, with the same rules of flavor number
assignment as there is for program number assignment. The "flavor"
of a credential or verifier refers to the value of the "flavor" field
in the opaque_auth structure. Flavor numbers, like RPC program
numbers, are also administered centrally, and developers may assign
new flavor numbers by applying through electronic mail to
"rpc@sun.com". Credentials and verifiers are represented as variable
length opaque data (the "body" field in the opaque_auth structure).
In this document, two flavors of authentication are described. Of
these, Null authentication (described in the next subsection) is
mandatory - it must be available in all implementations. System
authentication is described in Appendix A. It is strongly
recommended that implementors include System authentication in their
implementations. Many applications use this style of authentication,
and availability of this flavor in an implementation will enhance
interoperability.
Srinivasan Standards Track [Page 12]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
9.1 Null Authentication
Often calls must be made where the client does not care about its
identity or the server does not care who the client is. In this
case, the flavor of the RPC message's credential, verifier, and reply
verifier is "AUTH_NONE". Opaque data associated with "AUTH_NONE" is
undefined. It is recommended that the length of the opaque data be
zero.
10. RECORD MARKING STANDARD
When RPC messages are passed on top of a byte stream transport
protocol (like TCP), it is necessary to delimit one message from
another in order to detect and possibly recover from protocol errors.
This is called record marking (RM). One RPC message fits into one RM
record.
A record is composed of one or more record fragments. A record
fragment is a four-byte header followed by 0 to (2**31) - 1 bytes of
fragment data. The bytes encode an unsigned binary number; as with
XDR integers, the byte order is from highest to lowest. The number
encodes two values -- a boolean which indicates whether the fragment
is the last fragment of the record (bit value 1 implies the fragment
is the last fragment) and a 31-bit unsigned binary value which is the
length in bytes of the fragment's data. The boolean value is the
highest-order bit of the header; the length is the 31 low-order bits.
(Note that this record specification is NOT in XDR standard form!)
11. THE RPC LANGUAGE
Just as there was a need to describe the XDR data-types in a formal
language, there is also need to describe the procedures that operate
on these XDR data-types in a formal language as well. The RPC
Language is an extension to the XDR language, with the addition of
"program", "procedure", and "version" declarations. The following
example is used to describe the essence of the language.
11.1 An Example Service Described in the RPC Language
Here is an example of the specification of a simple ping program.
program PING_PROG {
/*
* Latest and greatest version
*/
version PING_VERS_PINGBACK {
void
PINGPROC_NULL(void) = 0;
Srinivasan Standards Track [Page 13]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
/*
* Ping the client, return the round-trip time
* (in microseconds). Returns -1 if the operation
* timed out.
*/
int
PINGPROC_PINGBACK(void) = 1;
} = 2;
/*
* Original version
*/
version PING_VERS_ORIG {
void
PINGPROC_NULL(void) = 0;
} = 1;
} = 1;
const PING_VERS = 2; /* latest version */
The first version described is PING_VERS_PINGBACK with two
procedures, PINGPROC_NULL and PINGPROC_PINGBACK. PINGPROC_NULL takes
no arguments and returns no results, but it is useful for computing
round-trip times from the client to the server and back again. By
convention, procedure 0 of any RPC protocol should have the same
semantics, and never require any kind of authentication. The second
procedure is used for the client to have the server do a reverse ping
operation back to the client, and it returns the amount of time (in
microseconds) that the operation used. The next version,
PING_VERS_ORIG, is the original version of the protocol and it does
not contain PINGPROC_PINGBACK procedure. It is useful for
compatibility with old client programs, and as this program matures
it may be dropped from the protocol entirely.
11.2 The RPC Language Specification
The RPC language is identical to the XDR language defined in RFC
1014, except for the added definition of a "program-def" described
below.
program-def:
"program" identifier "{"
version-def
version-def *
"}" "=" constant ";"
version-def:
"version" identifier "{"
Srinivasan Standards Track [Page 14]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
procedure-def
procedure-def *
"}" "=" constant ";"
procedure-def:
type-specifier identifier "(" type-specifier
("," type-specifier )* ")" "=" constant ";"
11.3 Syntax Notes
(1) The following keywords are added and cannot be used as
identifiers: "program" and "version";
(2) A version name cannot occur more than once within the scope of a
program definition. Nor can a version number occur more than once
within the scope of a program definition.
(3) A procedure name cannot occur more than once within the scope of
a version definition. Nor can a procedure number occur more than once
within the scope of version definition.
(4) Program identifiers are in the same name space as constant and
type identifiers.
(5) Only unsigned constants can be assigned to programs, versions and
procedures.
Srinivasan Standards Track [Page 15]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
APPENDIX A: SYSTEM AUTHENTICATION
The client may wish to identify itself, for example, as it is
identified on a UNIX(tm) system. The flavor of the client credential
is "AUTH_SYS". The opaque data constituting the credential encodes
the following structure:
struct authsys_parms {
unsigned int stamp;
string machinename<255>;
unsigned int uid;
unsigned int gid;
unsigned int gids<16>;
};
The "stamp" is an arbitrary ID which the caller machine may generate.
The "machinename" is the name of the caller's machine (like
"krypton"). The "uid" is the caller's effective user ID. The "gid"
is the caller's effective group ID. The "gids" is a counted array of
groups which contain the caller as a member. The verifier
accompanying the credential should have "AUTH_NONE" flavor value
(defined above). Note this credential is only unique within a
particular domain of machine names, uids, and gids.
The flavor value of the verifier received in the reply message from
the server may be "AUTH_NONE" or "AUTH_SHORT". In the case of
"AUTH_SHORT", the bytes of the reply verifier's string encode an
opaque structure. This new opaque structure may now be passed to the
server instead of the original "AUTH_SYS" flavor credential. The
server may keep a cache which maps shorthand opaque structures
(passed back by way of an "AUTH_SHORT" style reply verifier) to the
original credentials of the caller. The caller can save network
bandwidth and server cpu cycles by using the shorthand credential.
The server may flush the shorthand opaque structure at any time. If
this happens, the remote procedure call message will be rejected due
to an authentication error. The reason for the failure will be
"AUTH_REJECTEDCRED". At this point, the client may wish to try the
original "AUTH_SYS" style of credential.
It should be noted that use of this flavor of authentication does not
guarantee any security for the users or providers of a service, in
itself. The authentication provided by this scheme can be considered
legitimate only when applications using this scheme and the network
can be secured externally, and privileged transport addresses are
used for the communicating end-points (an example of this is the use
of privileged TCP/UDP ports in Unix systems - note that not all
systems enforce privileged transport address mechanisms).
Srinivasan Standards Track [Page 16]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
REFERENCES
[1] Birrell, A. D. & Nelson, B. J., "Implementing Remote Procedure
Calls", XEROX CSL-83-7, October 1983.
[2] Cheriton, D., "VMTP: Versatile Message Transaction Protocol",
Preliminary Version 0.3, Stanford University, January 1987.
[3] Diffie & Hellman, "New Directions in Cryptography", IEEE
Transactions on Information Theory IT-22, November 1976.
[4] Mills, D., "Network Time Protocol", RFC 1305, UDEL,
March 1992.
[5] National Bureau of Standards, "Data Encryption Standard",
Federal Information Processing Standards Publication 46, January
1977.
[6] Postel, J., "Transmission Control Protocol - DARPA Internet
Program Protocol Specification", STD 7, RFC 793, USC/Information
Sciences Institute, September 1981.
[7] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
USC/Information Sciences Institute, August 1980.
[8] Reynolds, J., and Postel, J., "Assigned Numbers", STD 2,
RFC 1700, USC/Information Sciences Institute, October 1994.
[9] Srinivasan, R., "XDR: External Data Representation Standard",
RFC 1832, Sun Microsystems, Inc., August 1995.
[10] Miller, S., Neuman, C., Schiller, J., and J. Saltzer, "Section
E.2.1: Kerberos Authentication and Authorization System",
M.I.T. Project Athena, Cambridge, Massachusetts, December 21,
1987.
[11] Steiner, J., Neuman, C., and J. Schiller, "Kerberos: An
Authentication Service for Open Network Systems", pp. 191-202 in
Usenix Conference Proceedings, Dallas, Texas, February 1988.
[12] Kohl, J. and C. Neuman, "The Kerberos Network Authentication
Service (V5)", RFC 1510, Digital Equipment Corporation,
USC/Information Sciences Institute, September 1993.
Srinivasan Standards Track [Page 17]
RFC 1831 Remote Procedure Call Protocol Version 2 August 1995
Security Considerations
Security issues are not discussed in this memo.
Author's Address
Raj Srinivasan
Sun Microsystems, Inc.
ONC Technologies
2550 Garcia Avenue
M/S MTV-5-40
Mountain View, CA 94043
USA
Phone: 415-336-2478
Fax: 415-336-6015
EMail: raj@eng.sun.com
Srinivasan Standards Track [Page 18]